APPENDIX. 59 



of which the species are endo-parasitic in the larger Crustacea), 

 although they can feed, die after fertilizing the females ; while 

 the latter then take to a parasitic life, produce eggs, and continue 

 to live for some time. It is supposed that the dwarf male of 

 Bonellia viridis does not live so long by several years as the hun- 

 dred times larger female, and it too has no mouth to its alimentary 

 canal. These examples might be further increased by reference to 

 zoological literature. 



In most cases the female lives longer than the male, and this 

 needs no special explanation r but the converse relation is con- 

 ceivable, when, for instance, the females are much rarer than the 

 males, and the latter lose much time in seeking them. The above- 

 mentioned case of Aglia tau probably belongs to this category. 



We cannot always decide conclusively whether the life of one 

 sex has been lengthened or that of the other shortened ; both 

 these changes must have taken place in different cases. There is 

 no doubt that a lengthening of life in the female has arisen in 

 the bees and ants, for both sexes of the saw-flies, which are be- 

 lieved to be the ancestors of bees, only live for a few weeks. But 

 among the Strepsiptera the shorter life of the male must have been 

 secondarily acquired, since we only rarely meet with such an ex- 

 treme case in insects. 



NOTE 7. BEES. 



It has not been experimentally determined whether the workers, 

 which are usually killed after some months, would live as long as 

 the queen, if they were artificially protected from danger in the 

 hive ; but I think that this is probable, because it is the case 

 among ants, and because the peculiarity of longevity must be 

 latent in the egg. As is well known, the egg which gives rise to 

 the queen is identical with that which produces a worker, and 

 differences in the nutrition alone decide whether a queen or a 

 worker shall be formed. It is therefore probable that the duration 

 of life in queen and worker is potentially the same. 



NOTE 8. DEATH OF THE CELLS IN HIGHER ORGANISMS. 



The opinion has been often expressed that the inevitable appear- 

 ance of normal ' death ' is dependent on the wearing out of the 



